Silicon and oxygen are two of the most common elements on Earth. Together, they make up nearly 75 percent of the Earth's crust, so it is no surprise that they play major roles in forming many of the minerals that we see in rocks. The silicon atom, which has four electrons in its outermost region, likes to form chemical bonds with oxygen atoms, which are attracted to extra electrons. Thus, silicon and oxygen, together with some of the metallic elements, can combine to make hundreds of different minerals. For example, quartz has two oxygen atoms for every silicon atom, and feldspar has two or three silicon atoms grouped with eight oxygen atoms and a few metal atoms. About half of the most common minerals found on Earth belong to the silicate group, as do some beautiful gemstones such as amethyst, opal, and topaz.

Shiny metals have been associated with beauty and wealth throughout human history. Gold, silver, and copper are three of the few metals that sometimes occur uncombined with other elements in nature, so it was relatively easy for ancient humans to collect them for personal adornment and trading. Copper jewelry emerged about 7,000 years ago, and the Egyptians began to make gold jewelry between 3,000 and 5,000 years ago. In many cultures, people put much of their wealth into their jewelry, both metallic and non-metallic (stones and bones), and used it as currency before the idea of money developed. The first coins appeared in the areas now known as Turkey and Greece about 2,600 years ago. Over the centuries, humans added so-called "base" metals to the gold and silver in coins, whose value became determined by law, not the actual value of the metals in the coin. Today, a U.S. "copper" penny is 97.5 percent zinc with a thin coating of copper; higher-denomination coins have a copper core covered with a copper-nickel alloy.